Leroy Gordon Cooper, Jr., also noted as Gordo Cooper, (March 6, 1927 – October 4, 2004) was an engineer and American astronaut. Cooper was one of the seven original astronauts in Project Mercury, the first manned-space effort by the United States. He flew the longest spaceflight of the Mercury project, was the first American to sleep in orbit, and was the last American to launch alone into Earth orbit and conduct an entire solo orbital mission.

Cooper was born in Shawnee, Oklahoma. He grew up there and in Murray, Kentucky where he attended public schools. He was active in the Boy Scouts of America and achieved the second highest rank of Life Scout. Cooper served in the Marine Corps in 1945 and 1946, then received an Army commission after completing three years of coursework at the University of Hawaii. Cooper met his first wife Trudy (the only wife of a Mercury astronaut with a private pilot's license) while in Hawaii and they married in 1947. Cooper transferred his commission to the Air Force in 1949, was placed on active duty and received flight training at Perrin AFB, Texas and Williams AFB, Arizona.

Cooper's first flight assignment came in 1950 at Landstuhl, West Germany where he flew F-84 Thunderjets and F-86 Sabres for four years. While in Germany he also attended the European Extension of the University of Maryland. Returning to the United States, he studied for two years at the Air Force Institute of Technology in Ohio and in 1957 completed his bachelor's degree in aerospace engineering. Cooper was then assigned to the Experimental Flight Test School at Edwards Air Force Base in California and after graduation was posted to the Flight Test Engineering Division at Edwards where he served as a test pilot and project manager testing the F-102A and F-106B. Cooper logged more than 7,000 hours of flight time, with 4,000 hours in jet aircraft. He flew all types of commercial and general aviation airplanes and helicopters.